Room temperature spectroscopy is a long-sought application for radiation detection, which historically has required operation of detectors at cryogenic temperatures (e.g. less than 77 Kelvin) for semiconductor devices. The development of detectors capable of reliably and sensitively detecting radiation of a particular type has required development of new materials to avoid the undesirable power and practical constraints imposed by cryogenic operation. One detector employed today for room temperature spectrometry is a thallium bromide-based material (TlBr).
However, TlBr-based compounds suitable for use as radiation detectors, particularly gamma detectors, are subject to rapid degradation and damage. The TlBr detectors are typically soft, and thus subject to mechanical damage, as well as sensitive to oxidation and other chemical reactions with the surrounding environment. Notably, biased TlBr detectors degrade in the presence of air, and even more rapidly in an environment of nitrogen gas, ultimately resulting in formation of thallium metal pathways on the detector surface. As TlBr is a semiconductor, but Tl is a conductor, the conductive pathways formed from Tl are more conductive than the TlBr bulk, and tend to short out the detector. Such shorts render the detector useless in its intended application.
Application of a bias to TlBr-based detectors, as is performed during detection of target radiation, accelerates the degradation of the detector. This phenomenon is expected due to the nature of TlBr as an ionic conductor.
Accordingly, to improve the longevity of TlBr-based detector compositions, conventional techniques involve the use of Tl metal-based electrodes on the detector, optionally coupled with switching the voltage polarity after some small period of time, typically 24 hrs. Additionally or alternately, replacing some or all of the Br at the surface of the detector with an alternate halogen, e.g. F, Cl, or I, has been employed to facilitate greater longevity of TlBr-based detectors.
However, using Tl-based electrodes and switching the voltage polarity only modestly extends the longevity of the detector, while the inventors of the presently disclosed inventive concepts discovered that surfaces incorporating a halogen other than or in addition to Br degrade more rapidly than the TlBr-based bulk material when exposed to air or nitrogen. Since room temperature (e.g. 22-27° C.) is the temperature of operation for most applications to which TlBr-based detectors are particularly suited, and this ability to operate at room temperature is the primary advantage of TlBr-based detectors, degradation of the type observed and shown in FIG. 1 is catastrophic.
Accordingly, it would be advantageous to provide techniques for forming TlBr-based detector structures that improve the longevity of the detector without introducing a tendency to form conductive pathways through the detector or on the detector surface in the presence of common atmospheric components such as nitrogen, oxygen, carbon dioxide, etc.